The intra-ocular pressure (TOP), i.e., the pressure within the eyeball, of a person is one of the most important parameters indicating the health status of the person's eye. Various eye diseases cause the TOP to be higher or lower than normal, but it is mainly elevated when the patient is suffering from glaucoma. Glaucoma is an extremely common condition afflicting about 2% of the population over 40 years of age and is one of the major causes of blindness in the world. This disease has no symptoms and is usually diagnosed by tonometry measuring the TOP of the subject. Tonometry is therefore a routine procedure in all eye examinations, especially those of adults.
There are various types of tonometers for measuring the TOP. One type, called an “indentation tonometer”, or “impression tonometer”, measures the TOP by measuring a deformation produced in the subject's cornea when a constant force is applied. However, the more common type is the “applanation tonometer”, which flattens the cornea and measures the force applied. The commonest and most reliable tonometer used at the present time is called the Goldmann applanation tonometer, in which a flat plate is pressed against the subject's cornea, and the area of applanation is viewed by means of a slit-lamp and microscope until the diameter of applanation is found to be 3.06 mm. Thus, it was found by Goldmann that at an applanation diameter of 3.06 mm (or an applanation area of 7.35 mm2), the force required to distort the cornea from its convex shape to a flat shape counterbalances the surface tension effect of the tear-film of the subject, such that when using this applanation diameter, the force in grams multiplied by “10” is directly converted to the TOP in mm of Hg.
In the Goldmann tonometer, the applanation area is measured by optically splitting it into two halves by a biprism, one half being displaced 3.06 mm relative to the other. A fluorescent solution is first applied to the eye to form a ring which is seen as two semi-circles. A control (e.g. a manually rotatable dial) is used to apply a flattening force to the subject's cornea. When the two semi-circular rings touch, the position of the dial, calibrated in mm Hg, indicates the force required to produce an applanation diameter of 3.06 mm.
Tonometer devices in general, and applanation tonometry devices in particular, may be classified either as (i) slit-lamp-mounted tonometers (for example, the Goldmann tonometer slit-lamp apparatus in FIG. 1) and (ii) portable tonometers (for example, the Perkins tonometer illustrated in FIG. 2). Both the Goldmann and Perkins tonometry devices have been widely used for detecting glaucoma and for evaluating patients with glaucoma for decades.
There is an ongoing medical need for improved tools and methods for detecting and monitoring glaucoma. In particular, there is an ongoing medical need for improved tonometry device and methods.
A Discussion of Goldmann Tonometry Devices and of Slit-Lamp Devices
FIG. 1 is a drawing of a conventional slit-lamp Goldmann applanation tonometry system for measuring an intraocular pressure of a patient's eye. At a time when the face of the patient 180 is immobilized in the rectangular-shaped face-immobilizing-frame 120 including substantially-horizontal chin rest 90, medical attendant 190 controls the position of tonometry probe 110 using a mechanical controller 30 to move the distal tip of probe 110 into contact with the patient's cornea. Horizontal-orientation-constrained probe 110 is mounted to the biomicroscopy device so that its orientation is mechanically constrained in a ‘horizontal’ orientation/horizontal local plane perpendicular to a gravity vector.
As is illustrated in FIGS. 1 and 4, the examination is carried out when patient is sitting. Thus, the examination is carried when the head of the patient 180 is oriented so that an inter-pupillary vector connecting his/her eyes is horizontal and/or is co-planar with the inter-pupillary vector connecting the eyes of medical attendant 190.
As shown in FIG. 3, light incident upon the patient's cornea at the time of contact between a distal end of probe 110 and the patient's cornea enters into tonometry probe 110 and traverses the tonometry probe in a ‘proximal direction.’ After traversing the tonometry probe 110, this light continues in the ‘proximal’ direction until it enters into microscope assembly 40. The location at which the distal end of the tonometry probe contacts the cornea of the patient 190 is in the field of view of the microscopy assembly and is viewable by medical attendant 190—for example, as semi-circles.
Because tonometer probe 110 points away from attendant 190 and towards patient 180, the ‘proximal’ and ‘distal’ ends of the proximal-distal vector of FIGS. 1 and 4 (this vector happens to be substantially horizontal) are labeled such that ‘proximal’ means closer to attendant 190, while ‘distal’ means farther from attendant 190 (and closer to the eye of patient 180). Horizontal-orientation-constrained tonometry probe 110 points ‘away from’ attendant 190 and to patient 180—thus, the proximal-distal vector of probe 110 of FIGS. 3 and 5A correspond to the proximal-distal vector of FIGS. 1 and 4.
In FIGS. 1-4 two horizontal directions are illustrated—the ‘lateral direction’ which corresponds to attendant's left and right, and the ‘longitudinal direction’ which is the vector from attendant 190 to the patient 180 and/or coincides with the vector from a centroid of microscope assembly 40 and tonometry probe 110 and/or coincides the ‘proximal-distal’ vector. As will be discussed below (see, for example, FIGS. 9-11 and the accompanying discussion), conventional slit lamp devices and Goldmann applanation tonometry devices are constructed so that the set of possible ‘longitudinal,’ ‘lateral’ and ‘vertical’ positions of a distal end (i.e. a centroid of the distal end) of tonometry probe are range-bound.
Typically, Goldmann applanation systems are provided as ‘add-ons’ to a biomicroscopy slit-lamp device and can be reversibly mounted to the slit-lamp device. Commercially, a number of vendors sell slit-lamps and Goldmann applanation assemblies separately. Thus, it may be said that the slit-lamp biomicroscopy device and the Goldmann applanation system of FIG. 1 ‘share’ a common illumination source (i.e. slit-lamp 70 light of illumination column which emits a substantially-vertical narrow beam of light) and a common microscope assembly 40. The ‘common components’ may be used either to measure the patient's IOP when in ‘Goldmann tonometry mode’ or for other biomicroscopy functionality.
FIG. 1 illustrates a conventional slit-lamp Goldmann applanation system when the Goldmann applanation assembly is mounted to the slit-lamp. FIG. 4 illustrates the slit lamp in the absence of the Goldmann applanation ‘add-on’ assembly—i.e. when the Goldmann applanation assembly is not mounted to the slit lamp.
The conventional slit-lamp apparatus of FIGS. 1 and 4 includes: (i) a lower base 10—for example, including a table-top as illustrated, (ii) an upper base 20 or carriage which is movable (for example, slidable or glidable or otherwise movable) over the surface of the lower base 10; (iii) microscope assembly 40 which supported by microscope support arm 50; and (iv) an illumination column including slit-lamp light 70.
In the example of FIG. 1, upper base (carriage) 20 bears the weight of the microscopy assembly 40 and the illumination column via base column 22, and horizontal motion (i.e. lateral or longitudinal) of the upper base 20 over the lower base 10 causes ‘in-tandem’ motion of the both the microscope assembly 40 and the illumination column. For the specific system illustrated in FIGS. 1 and 4, there are two ways to horizontally move the upper base (carriage) 20 over the surface of the lower base: (i) a ‘coarse-movement’ mode whereby the medical attendant (or anyone else) may directly place his/her hands on upper base (carriage) 20 and directly move upper base (carriage) 20 horizontally; and (ii) a ‘fine-movement mode’ regulated by a manual or motorized control 30 such as a joystick.
When the Goldmann tonometry assembly including probe 110 and spring-container 108 is mounted to the slit-lamp (e.g. via port 102), the position of the probe 110 is fixed relative to movable carriage 20 at a time when the device is operated. Because both probe 110 as well as microscope assembly 40 are both mounted to upper base (carriage) 20, the probe 110 and microscope assembly 40 move horizontally in tandem with each other (for example, in ‘fine-movement’ mode (i.e. using control 30) or in ‘coarse-movement mode). Furthermore, probe 110 is mounted to the slit-lamp and to movable upper base (carriage) 20 such that the probe 110 and microscope assembly 40 move vertically in tandem—for example, by raising or lowering an upper surface of base-column 22 which bears the weight of both microscope assembly 40 and probe 110.
For this purpose, a ‘vertical motion controller’ that is either separate from the horizontal motion controller 30 or the same as (i.e. in a ‘dual-mode controller) horizontal motion controller 30.
In particular implementations, microscope assembly 40 and/or probe 110 also move horizontally and/or vertically ‘in-tandem’ with slit-lamp light 70, passive optical component(s (e.g. minor) configured to re-direct a beam of light from a substantially vertical to a substantially horizontal direction.
The position of face-immobilizing-frame 120 is rigidly fixed relative to the lower base 10 so that vertical and/or horizontal motion of upper base (carriage) 20 relative to lower base 10 moves probe 110 relative to the fixed-position face-immobilizing-frame 120. When the patient 180 places his/her face over chin rest 90, the elevation of his/her face and the height of his/her eyes is fixed. Motion of the distal end of horizontal-orientation-fixed probe 110 (and hence ‘in-tandem’ horizontal and vertical motion of microscopy assembly 40) relative to the patient's eyes is provided using one or more controller(s) 30. As explained below, in Goldmann tonometry devices, both horizontal and vertical-motion is range-limited.
FIGS. 5A-5C illustrates some exemplary Goldmann tonometry assemblies and components thereof. In FIG. 5A, tonometry probe 110 is connected, via probe arm 106 to spring-loaded control container 108 (e.g. box) which urges tonometry probe 110 forward (i.e. in the ‘distal direction’) with an amount of force controllable by spring control/knob 116. In the example of FIG. 5A, spring-loaded controller 108 is connected to the Goldmann tonometry port 102 via a mediating attachment element 104. As illustrated in FIG. 5B, tonometry probe 110 includes a central axis 114 and is attached to probe arm 106 via socket 112. FIG. 6 is a top view of the device of FIG. 1.
FIGS. 7-8 illustrate additional configurations whereby a tonometry probe is mounted directly or indirectly to a slit lamp device and/or a movable carriage 20 so that the probe position and orientation relative to microscope assembly 40 is fixed for in-tandem horizontal and vertical motion and/or so that probe 110 move ‘in-tandem’ with microscope assembly 40 and/or with other component(s). FIG. 7B illustrates the tonometry assembly in isolation; FIGS. 7A and 7C illustrate the same tonometry assembly mounted to the slit-lamp.
For the examples of FIGS. 5A-5B and 7B, it is observed that (i) Goldmann probe 110 is mechanically constrained in a horizontal orientation; (ii) an elevation difference between Goldmann probe 110 and spring-loaded controller 108 (or springs thereof) is mechanically constrained and fixed; (iii) probe 110 is mounted to the biomicroscopy device and/or carriage 20 and/or slit-lamp device via spring-loaded controller 108. and (iv) probe 110 is not housed in a common housing with spring-loaded controller 108—instead, probe 110 (i.e. within socket or probe-holder 112) is housed separately from spring-loaded controller 108 and connected to spring-loaded controller 108 via probe arm 106 for transmitting forces which is also ‘external’ to housing of spring-loaded controller 108.
In the examples of FIGS. 1 and 7 the probe may be said to be ‘hanging’ from the slit lamp—in FIG. 1 spring-loaded controller 108 (i.e. which supports tonometry probe 110) is hanging from the slit lamp, and in FIG. 7 probe 110 is ‘hanging’ from a higher element which rests atop the slit-lamp. Thus, in some examples, the tonometry probe may be said to be hanging. In contrast, in FIGS. 8A-8B the tonometry probe is suspended above a spring-loaded controller 108 which rests upon a portion of the slit lamp. Both the ‘hanging’ and ‘non-hanging’ cases provide in-tandem vertical and horizontal motion between the microscope 40 and the probe 110—in both cases, carriage 20 bears the weight of both microscope 40 and probe 110.